1. Field of the Invention.
The present invention relates to a replica plating device and its method of use, and more particularly, concerns such a device and its method for obtaining print-replicas of cells or the like from the surface of a culture medium within an open-ended container such as a petri dish.
2. Description of the Prior Art.
Laboratory investigations and research on cells are facilitated by the replication and subsequent identification of the cells of interest. It is often desirable to clone these cells which have certain characteristics in order to produce abundant quantities for the specific investigations relating to those cells. One technique for topographically duplicating colonies of cells and for conducting tests to duplicate select colonies is known as replica plating.
In the replica plating technique, an array of cell colonies is typically printed on a culture medium such as sterile agar medium. The array of cell colonies may consist of a pre-arranged pattern of spots printed on the agar surface, with sufficient clearance between each spot of cells to allow the diameter of the spot to grow as the number of cells therein replicate. Typically, the array may consist of 96, 108 or 144 spots of cells arranged in orthogonal rows and columns. For the replica plating transfer to occur, a replica filter, such as a Whatman filter paper, is placed over the colonies of cells and a replica plating tool is used to apply slight pressure against the filter paper. This pressure causes transfer of the array of cell colonies from the agar medium to the filter paper. Once the cell colonies have been print-plated onto the filter paper, the cell colonies can then be again replicated from this filter paper onto the surface of another agar medium or onto another filter. These transfers permit screening of the cell colonies to isolate those cells of interest. Since the replica plating provides for the transfer of colonies in the same pattern that the original colonies were incubated, ready identification of the source of cells of interest is the advantageous by-product of this technique.
Various replica plating procedures have been described in the following publications: Hirschberg, J. and Marcus, M., "Isolation by a Replica-Plating Technique of Chinese Hamster Temperature-Sensitive Cell Cycle Mutants," Journal of Cellular Physiology, 113:159-166 (1982); Klebe, R.J. et al., "Replica Plating of Cultured Mammalian Cells," Somatic Cell Genetics, Vol. 7, No. 3 pages 271-280 (1981); Gergen, J.P. et al., "Filter Replicas and Permanent Collections of Recombinant DNA Plasmids," Nucleic Acids Research, Vol. 7, No. 8, pages 2115-2136, (1979); and Suzuki, F. et al., "A Replica Plating Method of Cultured Mammalian Cells for Somatic Cell Genetics," Experimental Cell Research, Vol. 68, pages 476-479, (1971).
A typical replica plating tool, presently known and used, is disclosed in Molecular Cloning by T. Maniatis, published by Cold Spring Harbor Laboratory, 1982, page 306. This known and used replica plating tool resembles a hand-stamping instrument with a bottom pressure surface and an upwardly extending post for hand gripping. The bottom pressing surface includes a velvet layer to cushion the pressure of the filter paper against the cell colonies on the culture medium. To control the depth to which the known replica plating tool can penetrate into a petri dish, a horizontal depth stop is provided. Adjustment of this depth stop, due to its horizontal or lateral position, is awkwardly accomplished; further, there is some doubt that the known replica plating tool insures preservation of sterility in the petri dish from which the cell colonies are plate printed. Accordingly, there is a need to improve the characteristics of such a replica plating tool particularly for ease of use, the time required for use and degree of skilled involved, as well as improvements in sterility capabilities and disposability after a single use. One object of the present invention is the satisfaction of the needs perceived for such a replica plating tool.